i recommend replacing them because its a wear item. if you didnt have the transmission when it had zero miles on it, you have no idea of its history. maybe the original owner neglected it and ran the trans dry or low a time or two. or maybe they towed 4 times the rated capacity of the vehicle, or even raced the crap out of it while manually shifting at high RPMs.

regardless of how rare they need changing, youve already got the case open and replacing everything else, why not the washers and bearings ? to me, its an insurance thing, i suppose.